Unique dosage forms, manufactured as osmotic delivery systems entered the fields of medicine and pharmacy with the invention of osmotic delivery systems by inventors Theeuwes and Higuchi as disclosed in U.S. Pat. Nos. 3,845,770 and in 3,916,899. The osmotic systems disclosed in these patents comprise a semipermeable membrane that surrounds a compartment containing a therapeutic agent. The membrane is permeable to the passage of an external fluid, and it is substantially impermeable to the passage of drug. There is at least one exit through the membrane for delivering the therapeutic agent from the osmotic dosage form.
A pioneering advancement in osmotic delivery systems in the dispensing arts was presented in U.S. Pat. No. 4,327,725 by patentees Cortese and Theeuwes. This invention provides an osmotic delivery system for delivering a therapeutic agent that, because of its solubility in aqueous and biological fluids is difficult to deliver in meaningful amounts at a controlled rate over time. The osmotic delivery system of this patent comprises a semipermeable wall that surrounds a compartment containing a therapeutic agent that is insoluble to very soluble in aqueous and biological fluids, and an expandable hydrogel. In operation, the hydrogel expands in the presence of an external fluid that is imbibed into the delivery system and pushes the therapeutic agent from the delivery system, through an exit passageway.
A further contribution to the delivery arts in an inventive delivery system disclosed in U.S. Pat. No. 5,023,088 by patentees Wong, Theeuwes, Eckenhoff, Larsen, and Huynh. In this patent, the patentee disclosed a delivery system that comprises a semipermeable housing member with a compartment that contains a plurality of movable therapeutic units. The patentees disclosed further a driving member for displacing the therapeutic units through an opened orifice formed in the housing members, when the delivery system is in operation in an environment of use.
It will be appreciated by those skilled in the dispensing art, that the above disclosed dosage forms have a positive inventive value and they represent a practical and useful advancement in the dispensing art. Also, while the above described dosage forms possess ideal kinetics useful for delivering numerous and different drugs and at a controlled and continuous rate to many environments of use, there is an instance where the o manufacturer of these dosage forms can be improved to lead to more desirable results. For example, the dosage forms of the prior art are manufactured by a process of membrane coating wherein an organic solvent such as acetone or methylene chloride is used to coat the membrane onto the dosage form. While these solvents form excellent membranes, there are serious shortcomings associated with their use. That is, these organic solvents are expensive, they are explosive, traces can be possibly toxic, and during processing solvent fumes can escape and cause environmental concern. The conditions needed for optimizing production to produce a thin or a thick membrane often become impractical in mass production as variability between membrane weight and thickness uniformity can lead to differences in release profiles of the dosage form. Further, the optimization of coating conditions are very costly of each successive layer scale and production of a thick membrane often becomes impractical in mass production due to extremely long coating time. In addition, some special shapes of membrane could not be fabricated by coating process because of its complex in geometry.
It will be appreciated by those skilled in the dispensing art, that if a dosage form can be provided that exhibits a high level of reliable dispensing activity and is manufactured by a process that overcomes the shortcomings and disadvantages associated with the prior art, such a dosage form and its accompanying manufacturing process would have a positive value and also represent an advancement in the dispensing art. It well be immediately appreciated also by those skilled in the dispensing art that is a dosage form designed as an osmotic essentially free from organic solvents, such a dosage form would find a practical application in the fields of pharmacy and medicine. Likewise, it will be appreciated by those skilled in the art that if a novel composition is provided for injection-molding that lessens the problems known heretobefore, such a composition would represent a positive advancement in the art.